TRIMESTER SPECIFIC REFERENCE INTERVALS OF THYROID FUNCTION

TESTS AMONG NIGERIAN PREGNANT WOMEN

Jibril M. El-Bashir, Randawa A.J, Abbiyesuku F.M, Aliyu I.S, Akuyam S.A, Manu M, Adamu R, Suleiman

H.M, Yusuf R, Mohammed A.

INTRODUCTION• Thyroid disorders in pregnancy are harmful to maternal and foetal

health.• Pregnancy has a profound impact on thyroid gland and thyroid

function.• Normal pregnancy results in a number of hormonal changes that

affect thyroid function.• hCG (a weak thyroid stimulator)surge in 1st trimester and

supresses TSH.• Rise in oestrogen stimulates TBG synthesis with increase in T3 and

T4 . • Measurement of free thyroid hormones not total is necessary in

pregnancy.

SIMILARITIES IN CLINICAL PRESENTATION WITH NORMAL PREGNANCY

HYPERTHYROIDISM• Anxiety• palpitations• dyspnoea• sweating• heat intolerance• weakness• irritability• cardiac systolic murmurs

HYPOTHYROIDISM• Lethargy• weight gain• constipation

NEED FOR PREGNANCY REFERENCE INTERVALS

• American Thyroid Association (ATA) recommends Establishment of Trimester Specific Reference Intervals by each laboratory for proper interpretation

• If that is not possible, clinicians should use 0.1 – 2.5, 0.2 – 3.0 and 0.3 – 3.0 µIU/ml for TSH during 1st, 2nd and 3rd trimesters respectively.

AIM

• To establish trimester-specific thyroid function reference intervals in pregnancy among Nigerian pregnant population.

METHODOLOGY

• Three-hundred apparently healthy pregnant women were recruited into the study.

• Ages ranged between 14 – 40 years.• Thyroid function tests (TSH, free T4, free T3 and

TBG) were assayed using ELISA kits.• Trimester-specific reference intervals (2.5th and

97.5th centiles) were calculated for 1st , 2nd and 3rd trimesters’ respectively after log transformation using Microsoft Excel software 2007.

RESULTS

Trimester Specific Reference Intervals for TSH and Free T4 in subjects (2.5 and 97.5 percentiles)

• Subjects n TSH (µIU/L) Free T4 (ng/mL) • 1st trimester 75 (0.03 – 2.41) (0. 84 – 2.06)

• 2nd trimester 125 (0.14 – 3.55) (0.76 – 2.08)

• 3rd trimester 100 (0.21 – 3.12) (0.70 – 1.70)

RESULTS

Trimester Specific Reference intervals for Free T3 and TBG in subjects (2.5 and 97.5 percentiles)

• Subjects n Free T3 (pg/mL) TBG µg/mL

• 1st trimester 75 (1.92 – 3.51) (11.32 – 43.17)

• 2nd trimester 125 (1.65 – 3.96) (14.51 – 72.86)

• 3rd trimester 100 (1.74 - 3.65) (20.33 – 72.55)

DISCUSSION

• Establishment of local reference values in pregnancy is imperative for accurate diagnosis.

• In this study, TSH mirrored the change in free T4 • The values obtained here agree with ATA

suggested values and also with those obtained by Panesar et al 2001, Haddow et al 2004, Stricker et al 2007 and Bocos – Terraz et al 2009.

cont

• Samples from 120 reference individuals was recommended by IFCC as minimum for establishment of reference values.

• However, it was demonstrated by Horn et al 1998, Haddow et al 2004, Horrowitz et al 2008, and that less than 120 samples can be used.

• This is an important limitation of the study.

CONCLUSION

• Thyroid disease in pregnancy is common, clinically important and time sensitive.

• Hence, this study established Trimester specific thyroid function reference intervals for Nigerian pregnant population.

REFERENCES

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